Memory for a recent event can be expressed through explicit recollection or inferred from priming effects that need not involve intentional recollection of any previous experience. The latter kind of memory has been referred to as implicit memory. The goals of this project are to deepen and broaden our knowledge of implicit memory, to evaluate empirically relevant theoretical ideas put forward by the investigators, and to bring together ideas and findings concerning the nature of memory and perception. The experiments focus on priming of novel visual objects, and test the idea that such priming effects are mediated by a presemantic structural description system that represents information about the global relations among parts of objects. A total of 30 experiments and subexperiments are proposed. In Experiments 1a/b-2a/b, priming is examined with a possible/impossible object decision test, and predictions made by the structural description system hypothesis concerning the differential effects of semantic and structural encoding on implicit and explicit memory are evaluated. Experiments 3a/b-4a/b explore conditions under which priming of impossible objects may be obtained. Experiments 5-14 elucidate the nature of the structural descriptions underlying object decision priming using a new type of object decision task, and introduce new analytic paradigms that test the idea that the structural description system represents relations among parts with respect to an object's principal axis. Experiments 15-21 examine object priming in patients with organic amnesia, and provide tests of ideas concerning the neural locus of priming. The proposed research will enrich our knowledge of normal memory processes and also have important implications for understanding preserved and impaired memory functions following brain damage.